Lysosomal phospholipases A1 and A2 of bovine adrenal medulla.
1. [(32)P]Lecithin and [(32)P]phosphatidylethanolamine were prepared by incubating rat liver mince with [(32)P]phosphate. With these (32)P-labelled phospholipids conditions for the quantitative assay of phospholipase A activity were established. 2. The distribution of phospholipase A activity between subcellular fractions of the bovine adrenal medulla was determined. Phospholipases A(1) and A(2), with pH optima at 4.2 and 6.5 respectively, were found in the large-granule fraction. By means of sucrose-density-gradient centrifugation it was shown that both these phospholipases were localized in lysosomes. 3. Lysosomal phospholipase A(1) catalysed the hydrolysis of [(32)P]lecithin and [(32)P]phosphatidylethanolamine at the same rate. The enzymic activity was inhibited by 70% in the presence of 10mm-calcium chloride. 4. Lysosomal phospholipase A(2) catalysed the hydrolysis of [(32)P]phosphatidylethanolamine more rapidly than it hydrolysed [(32)P]lecithin. The hydrolysis of [(32)P]phosphatidylethanolamine, but not that of [(32)P]lecithin, by phospholipase A(2) was activated by 0.8mm-calcium chloride. However, the hydrolysis of both substrates was inhibited by 8mm-calcium chloride. 5. The significance of the presence of phospholipase activity in lysosomes is discussed in relation to the functions of lysosomes in general and in the adrenal medulla.
D000313:Adrenal Medulla / Q000166:cytology / Q000201:enzymology*; D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D002417:Cattle; D002499:Centrifugation, Density Gradient; D003864:Depression, Chemical; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver; D008247:Lysosomes / Q000201:enzymology*; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010740:Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010759:Phosphorus Isotopes; D051381:Rats; D013268:Stimulation, Chemical
D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010759:Phosphorus Isotopes; D010740:Phospholipases; D002122:Calcium Chloride